Vapor generator

ABSTRACT

An improved marine vapor generator of the type which includes a reheater and the means for tempering the heating gases flowing toward the reheater. The tempering means operates to control the reheater outlet steam temperature during ahead operation and to protect the reheater tube metal during astern operation of the ship propulsion system. The tempering means includes a duct arranged to discharge a regulable quantity of heated combustion air into the heating gases flowing toward the reheater. An alternative arrangement uses unheated combustion air as the tempering agent. A third arrangement uses low temperature gases as the tempering agent and includes a gas recirculating fan.

United States Patent [72] lnventor Richard A. Grams Medina, Ohio [2l] Appl. No. 813,166 [22] Filed Apr. 3, 1969 [45]v Patented May 25, 1971 [73] Assignee The Babcock & Wilcox Company New York, N.Y.

[54] VAPOR GENERATOR 4 Claims, 3 Drawing Figs.

[52] 1.1.8. Cl 60/73, 122/479, 60/102, 60/104, 60/105 [51] Int. Cl Folk 7/16 [50] Field of Search 60/73, 102, 104; 122/479, 479A [56] References Cited UNITED STATES PATENTS 2,685,280 8/1954 Blaskowski.. 60/73X 2,830,440 4/1958 Durham 60/73 Primary ExaminerMartin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorney-J. Maguire ABSTRACT: An improved marine vapor generator of the type which includes a reheater and the means for tempering the heating gases flowing toward the reheater. The tempering means operates to control the reheater outlet steam temperature during ahead operation and to protect the reheater tube metal during astem operation of the ship propulsion system. The tempering means includes a duct arranged to discharge a regulable quantity of heated combustion air into the heating gases flowing toward the reheater. An alternative arrangement uses unheated combustion air as the tempering agent. A third arrangement uses low temperature gases as the tempering agent and includes a gas recirculating fan.

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INVENTOR. Richard A. Grams ATTORNEY VAPOR GENERATOR The invention relates to a ship propulsion system and more particularly to marine-type vapor generators equipped with a reheater and the means for controlling the temperature of the flue gases passing over the said reheater.

The reheating of steam between turbine stages is well recognized as a desirable step in obtaining the high efficiencies required of today s power plant systems, however, the application of the reheat principle to a ships propulsion system introduces certain factors which are not normally encountered in stationary installations. One such factor is the practice of excluding the reheat system from the steam cycle during astern operation, certain types of maneuvering and during inport operation of the ship's power plant.

Heat exchanger surface intended for the superheating or reheating of steam is normally located in zones where operating gas temperatures are far above recognized design temperature use limits for metals, however, such use is made possible by the cooling effect on the metal derived from steam passing through the tubes of these heat exchangers. A problem arises during astern operation, maneuvering and in-port operation when no steam is being passed through the reheater, thereby producing a condition where tube metal temperatures will exceed safe design limits unless remedial measures are taken. One manner of overcoming this problem has been to locate the reheater in one of two parallel gas passes and to provide dampers for preventing the flow of hot combustion gases over the reheater when the latter is not in use, as is shown in US. Pat. No. 3,280,559.

The present invention eliminates the requirement of parallel gas passes and the dampers in high gas temperature locations associated with these gas passes, and provides protection for a reheater by introducing a low temperature gaseous fluid into the heating gas stream ahead of the reheater, thereby lowering the gas temperature to an acceptably safe limit before it enters the reheater gas pass. The low temperature gaseous fluid may be combustion air taken from the air inlet duct or flue gas I taken from the gas stream either before or after the air preheater. This combustion air or flue gas is introduced into a convection gas pass at a position between the superheater and reheater gas passes, and combines with the heating gases being discharged from the superheater gas pass to lower the temperature of these heating gases prior to their entering the reheater gas pass.

A primary object of the invention is to provide reheater tube metal protection during astern operation, maneuvering and in-port operation when no steam is being passed through the reheater. This is achieved by introducing sufficient quantities of low temperature gaseous fluid into the convection gas pass so as to lower the temperature of the heating gases to a value commensurate with the allowable temperature use limits of the reheater tube metal.

Another object of the invention is to provide means for protecting the reheater metals without imposing a difficult or impossible control problem respecting the superheater steam temperature. This is accomplished by locating the mixing point of the low temperature gaseous fluid with the heating gases downstream, gas flowwise, of the superheater surface. It can be readily seen that if steam generating apparatus of the general type disclosed by applicant should have this mixing point upstream, gas flowwise, of all or part of the superheater surface, that superheater or part of it would be exposed to mass gas flows and temperatures that would differ substantially for astem and forward operation at equal firing rates. Obviously this would impose a most difficult operating burden on the system for controlling superheater steam temperature over the unit's load range.

A further object of the invention is the control of reheat steam temperature during normal ahead operation when steam is passed through the reheater by regulating the temperature of the heating gases entering the reheater gas pass. This is accomplished by controlling the quantity of flue gas or combustion air being introduced into the convection gas pass for mixing with the heating gases.

In the drawings:

FIG. I is a diagrammatic sectional side view of an improved vapor generator having steam lines from the generator connecting to the forward and astern turbine drives and using 5 combustion air as the low temperature gaseous fluid.

FIG. 2 is a partial diagrammatic side view showing an alternate source for the combustion air used as low temperature gaseous fluid in the vapor generator of FIG. 1.

FIG. 3 is a partial diagrammatic side view using flue gas as the low temperature gaseous fluid in the vapor generator of FIG. 1.

Referring to FIG. 1 there is shown a boiler setting comprising a front wall 11 and a rear wall 12 (not shown) and sidewalls l3 and 14. The setting is partitioned into a furnace chamber 15, a superheater gas pass 16, a convection gas pass 17 and a reheater gas pass 18 'which extends to an outlet gas pass 19. Furnace chamber is defined by sidewall 13 and sections of front and rear walls 11 and 12 and a partition wall 20 21 to the superheater gas pass 16. The furnace section of front wall 11 includes the windbox 22 and associated front wall openings 23 to accommodate the fuel burning equipment (not shown).

and sections of front and rear walls 11 and 12 and a partition wall 24 which has a staggered tube section forming a screened first inlet 25 to the convection gas pass 17. The superheater gas pass 16 contains the entire superheater heat exchanger surface composed of upright generally U-shaped tubes 26 spaced across the whole width of the gas pass and comprising a primary superheater 27 and a secondary superheater 28, serially arranged in that order in the direction of gas flow.

Convection gas pass 17 is a vertically elongated pass disposed intermediate of and laterally adjoining superheater gas pass 16 and reheater gas pass 18 and is defined by partition wall 24 and sections of front and rear walls 11 and 12 and a partition wall 29 which has a staggered tube lower section forming a screened outlet 30 and a staggered tube upper section forming a screened second inlet 31.

Reheater gas pass 18 is a vertically elongated pass adjacently parallel to convection gas pass 17 and defined by partition wall 29 and sections of front and rear walls 11 and 12 and sidewall 14. Reheater gas pass 18 includes a reheater 32 comprising sinuous tubes 33 forming a main tube bank 32A and an auxiliary tubebank 32B, both banks being disposed across the width of the gas passage. Inlet header 34 connects to the inlet end of tube bank 32B, intermediate header 35 connects to the outlet end of tube bank 328 and the inlet end of the tube bank 32A and outlet header 36 connects to the outlet end of tube bank 32A. The reheater gas pass 18 may also include other heat exchange surface, for example, the economizer 37 located downstream gas flowwise of reheater 32.

Outlet gas pass 19 is a vertically elongated gas pass located above and in communication with the outlet of reheater gas pass 18. The outlet gas pass 19 is associated with the gas side 38A of a regenerative-type air heater 38.

Air inlet duct 39 forms a passage having an inlet end 40 connected to a forced draft fan 41, and an outlet end 42 connected to the windbox 22. Air inlet duct 39 is associated with the air side 38B of regenerative air heater 38 and includes flow control dampers 45 located near the first outlet end 42 adjacent windbox 22.

Tempering duct 44 forms an interconnecting passage between the air inlet duct 39 and the convection gas pass 17, by having its inlet end 43 connected to air duct 39'at a point downstream air flowwise of air heater 38 and its discharge end 46 connected to the convection gas pass second inlet 31. Flow control dampers 47 are included in the tempering duct.

The steam generating and heating sections of the boiler include a steam drum 48, a collection header 49 and supply headers 50 and 51. For the sake of clarity, additional headers, risers, downcomers and the connecting steam piping between drum 48 and superheater headers 52A, 52B, 52C and 52D are 20 which has a staggered tube section forming a screened inlet The superheater gas pass 16 is defined by partition wall 20 not shown since the physical arrangement of these is conventional and not part of the invention, as such.

Steam supply line 53 connects the outlet header 52B to the inlet side of a forward drive high-pressure turbine 54. A steam supply auxiliary line 55 connects the inlet side of an astem drive high-pressure turbine 56 to the steam line 53. Shutoff valves 57 and 58 are located downstream flowwise of the juncture point between steam lines 53 and 55. A steam exhaust line 59 connects the outlet side of high-pressure turbine 54 to reheater inlet header 34 by way of line 60 and to reheater intermediate header 35 by way of line 61. Shutoff valves 62 and 63 are located in the lines 60 and 61, respectively. A steam supply line 64 connects the reheater outlet header 36 to the inlet side of a forward drive low pressure turbine 65. A crossover steam line 66 interconnects steam lines 59 and 64 and includes a shutoff valve 67. Steam line 64 includes a shutoff valve 68 located upstream flowwise of the crossover line 66. Steam exhaust lines 69 and 70 extending from the outlet end of turbines 56 and 65, respectively, discharge into a condenser (not shown).

Referring to FIG. 2 there is shown the upper end of reheater gas pass 18 which includes the economizer 37 and communicates with the outlet gas pass 19. The forced draft fan 41 connects for discharge into inlet 40 of the air inlet duct 39. Regenerative air heater 38 has its gas side 38A associated with the outlet gas pass 19 and its air side 38B associated with the air inlet duct 39.'A tempering duct 44A has its inlet end 43A communicating with the air inlet duct 39 at a point upstream air flowwise of the air heater 38 and an outlet end 46A discharging into convection gas pass 17 through screened second inlet 31. Flow control dampers 47A are located near the outlet end of the tempering duct. Included in this view is a showing of steam drum 48 and the upper portion of screened first inlet 25.

Referring to FIG. 3 there is shown the upper end of reheater gas pass 18 which includes the economizer 37 and communicates with the outlet gas pass 19. The forced draft fan 41 connects for discharge into inlet 40 of the air inlet duct 39. Regenerative air heater 38 has its gas side 38A associated with the outlet gas pass 19 and its air side 38B associated with the air inlet duct 39. A tempering duct 71 has its inlet end 72 communicating with the outlet gas pass 19 at a point downstream gas flowwise of the air heater 38, and its outlet end 78 discharging into convection gas pass 17 through screened second inlet 31. A fan 73 of the type used to recirculate flue gases is operatively associated with the tempering duct 71. Flow control dampers 74 disposed upstream of fan 73 are used to regulate the quantity of gas flowing through tempering duct 71. Gastight dampers 75 are arranged to close to prevent the reverse flow of gases when the fan 73 is shut down or inoperative. A seal air line 76 supplies pressurized air to the space between the dampers 75 and creates a pressure seal when these dampers are in their closed position. A shutoff valve 77 is included in the seal air line 76.

In the normal ahead or forward operation of the ship propulsion system, the steam-water fluid flow path through the vapor generator and associated turbines shown in FIG. 1 is as follows: A controlled quantity of feedwater is admitted to economizer 37 and is convectively heated by the flue gases flowing over the tubes. The heated water is then introduced in steam drum 48 to maintain a predetermined water level. A natural circulation cycle takes place whereby water from steam drum 48 is circulated through downcomers (not shown) to supply headers 50 and 51 etc. The water leaving the supply headers is heated, becoming a steam-water mixture during its passage upwardly through the tubes of front and rear walls 11 and I2, sidewalls l3 and 14 and partition walls 20, 24 and 29. The steam-water mixture is returned to steam drum 48 directly from the partition walls and enclosure walls. The saturated steam leaving drum 48 is conveyed through appropriate piping (not shown) to be passed serially through the primary and secondary superheaters 27 and 28. These superheater sections are arranged for series flow and may include an attemperator (not shown) between the primary superheater outlet header 52C and the secondary superheater inlet header 52A for superheated steam temperature control. The superheated steam upon leaving the secondary superheater outlet header 52B is conveyed by supply line 53 to the forward drive highpressure turbine 54, shutoff valve 58 being in a wide open position. Shutoff valve 57 in supply line 55 is in the closed position to prevent the flow of superheated steam to the astem drive turbine 56. Steam leaving the forward drive high-pressure turbine 54 is conveyed by exhaust line 59 to be selectively introduced into reheater 32 through the inlet header 34 and/or the intermediate header 35. This dual steam entry arrangement into the reheater offers a means of controlling the reheat steam temperature by varying the amount of reheater heating surface through which steam is being passed. Thus, the reheat outlet steam temperature may be increased by introducing all of the steam through inlet header 34 and passing it through banks 32B and 32A or, conversely, it may be reduced by introducing the steam through intermediate header 35 and passing it only through bank 32A. As will be observed it is also possible to pass steam in proportionate amounts into both headers 34 and 35 simultaneously. The reheated steam leaving the outlet header 36, is conveyed by supply line 64 to the forward drive low pressure turbine 65. Steam leaving turbine 65 discharges through exhaust line 70 is condensed and returned to the condensate system (not shown) for use as feedwater for the vapor generator.

During normal ahead or forward operation of the steam propulsion system, the steam-water fluid flow path for the vapor generator and turbines associated with the alternative arrangements shown in FIGS. 2 and 3 remain the same as that described in FIG. 1.

During normal astem operation of the ship propulsion system, the steam-water fluid flow path for the vapor generator and turbines shown in FIG. 1 differs from normal ahead or forward operation in that upon leaving secondary superheater 28, the steam is directed to a high-pressure condensing-type turbine 56, normally referred to as an astern turbine, and whose direction of rotation is opposite from that of turbine 54 which is used for ahead operation. Since for this service there customarily is no flow through the reheater, the steam leaving the astern turbine is condensed and returned to the condensate system (not shown) for use as feedwater for the vapor generator.

During normal astem operation of the ship propulsion system, the steam-water fluid flow path for the vapor generator and turbines associated with the alternative arrangements shown in FIGS. 2 and 3 will be the same as that described for FIG. 1.

In accordance with the present invention, during normal ahead and astem operation of the ship propulsion system, the combustion gas path for the vapor generator shown in FIG. 1 is as follows: The forced draft fan 41 supplies combustion air to the inlet end 40 of the air inlet duct 39, the combustion air is heated as it passes through the air side 38B of regenerative air heater 38. Depending on the position of the flow control dampers, a portion of the combustion air flowing in air inlet duct 39 downstream air flowwise of air heater 38 may be admitted through inlet 43 to the tempering duct 44, the remainder of the combustion air being regulated by the control dampers 45 for discharge through inlet 42 into the windbox 22. The combustion air is introduced through burner openings 23 to mix with the burning fuel and the resultant heating gases transfer a portion of their heat content to the water cooling tubes lining furnace enclosure 15, thereafter, the heating gases are discharged through screened inlet 21 into superheater gas pass 16 where heat from the gases is transferred to the superheater and saturated wall enclosure surfaces. From passage 16 the heating gases are discharged through screened first 25 into the convection gas pass 17. While in this convection gas pass, the heating gases mix with that portion of the combustion air which is being discharged from tempering duct 44 through the screened second inlet 31 and the resultant mixture of heating gases and air is directed downwardly toward screened outlet 30 with heat being transferred to a portion of the water cooled enclosure walls of passage 17. The gases discharging into reheater gas pass 18 are directed upwardly across reheater 32 and economizer 37 with heat being transferred to the reheater, the economizer and the saturated wall enclosure surfaces. The gases emerging from passage 18 discharge into the outlet gas pass 19 and flow through the gas side 38A of the air heater 38 wherein heat is transferred to that portion of air heater surface for subsequently raising the temperature of the incoming air when the surface is rotated to the air side 388.

During the normal ahead operation of the ship propulsion system, reheater outlet steam temperature is controlled by modulating the control dampers 47 thereby varying the quantity of air supplied and consequently the temperature of the heating gases and air mixture entering the reheater ga's pass 18, since the temperature of the air supplied via duct 44 is lower than the temperature of the combustion gas leaving screened inlet 25. A closing of dampers 47 will decrease the quantity of combustion air being admitted to gas passage 17 thus reducing the cooling effect of the air on the heating gases entering the gas pass 17, the combined flow of air and gas entering gas pass 18 resulting in a rise in reheat steam temperature for equivalent steam flows. The converse effects will result from an opening of the dampers 47 with the accompanying increase in the quantity of combustion air admitted to gas passage 17.

During astem operation of the ship propulsion system there will be no steam flow through the reheater 32 with the result that the tube metal temperature will closely approximate the temperature of the gases flowing past the reheater 32. It therefore becomes absolutely essential to limit the temperature of the gases entering the reheater gas pass 18 to safe allowable operating limits for tube metal temperature. The present invention accomplishes this by the opening of the control dam- I pers to admit sufficient combustion air into the convection gas pass 17 to reduce the temperature of the heating gases to the required limits.

During normal ahead and astem operation of the ship propulsion system, the combustion air and gas path for the vapor generator associated with the alternative arrangement shown in FIG. 2 will be the same as that described for FIG. 1, with the exception that the portion of combustion air being admitted to tempering duct 44A will be taken from the air flowing in air inlet duct 39 upstream air flowwise of air heater 38.

During normal ahead and astem operation of the ship propulsion system, the combustion air and gas path for the vapor generator associated with the alternative arrangement shown in FIG. 3 will be the same as that described for FIG. 1, with the following exceptions: All of the combustion air is delivered to the windbox 22 since the alternative arrangement does not have a tempering duct connected to the air inlet duct 39. A portion of relatively low temperature gases passing through the outlet gas pass 19 is directed into the tempering duct inlet end 72 located downstream flowwise of regenerative air heater 38. This portion of low temperature gases is conveyed by tempering duct 71 through the second inlet screen 31 into convection gas pass 17. The fan 73 provides the necessary suction and discharge pressures to maintain a positive flow of low temperature gases from the outlet gas pass 19 to the convection gas pass 17. Whenever fan 73 is not operating, the gas tight dampers 75 will be in a shut position and the seal air line shutoff valve 77 will be open to introduce pressurized air into the space between the dampers 75 thereby preventing any reverse flow of gases through tempering duct 71.

I claim:

1. In a ship propulsion system wherein superheated and reheated steam is selectively suppliedto a forward drive turbine and only superheated steam to an astem drive turbine, the combination with the propulsion system of a vapor generator comprising:

walls de rning a setting;

partition wall means dividing the setting into a furnace, a superheater gas pass laterally adjoining the furnace and arranged to receive all of the furnace gas outflow, a reheater gas pass, and a vertically elongated convection gas pass disposed intermediate and laterally adjoining the superheater and reheater gas passes and arranged for gas discharge through an outlet at the lower end portion of the reheater gas pass, said convection gas pass having adjacent first and second inlets at the upper end portion thereof, said first inlet being arranged to receive all of the gas outflow from the superheater gas pass;

an outlet gas pass arranged to receive all of the gas outflow from the reheater gas pass;

at least one bank of superheater tube banks positioned in the superheater gas pass;

a plurality of fluid heating tube banks including at least one reheater tube bank positioned in the reheater gas pass, said reheater tube bank being arranged upstream gas flowwise of the remaining fluid heating tube banks in said reheater gas pass;

firing means associated with said furnace to produce heating gases for flow through the setting;

a forced draft fan;

an air inlet duct connected to the forced draft fan for delivering combustion air to said firing means; and

tempering means for introducing a low temperature gaseous fluid through the second inlet of the convection gas pass, said tempering means including a tempering duct flowconnecting the air inlet duct to the second inlet of said convection gas pass.

2. A ship propulsion system according to claim 1 wherein the tempering duct includes a damper for regulating the quantity of flue gas passing therethrough.

3. A ship propulsion system according to claim 2 wherein the air inlet duct includes heat exchange means for heating the combustion air, the tempering duct being flow-connected to the air inlet duct downstream air flowwise of said heat exchange means.

4. A ship propulsion system according to claim 2 wherein the air inlet duct includes heat exchange means for heating the combustion air, the tempering duct being flow-connected to the air inlet duct upstream air flowwise of said heat exchange means. 

1. In a ship propulsion system wherein superheated and reheated steam is selectively supplied to a forward drive turbine and only superheated steam to an astern drive turbine, the combination with the propulsion system of a vapor generator comprising: walls defining a setting; partition wall means dividing the setting into a furnace, a superheater gas pass laterally adjoining the furnace and arranged to receive all of the furnace gas outflow, a reheater gas pass, and a vertically elongated convection gas pass disposed intermediate and laterally adjoining the superheater and reheater gas passes and arranged for gas discharge through an outlet at the lower end portion of the reheater gas pass, said convection gas pass having adjacent first and second inlets at the upper end portion thereof, said first inlet being arranged to receive all of the gas outflow from the superheater gas pass; an outlet gas pass arranged to receive all of the gas outflow from the reheater gas pass; at least one bank of superheater tube banks positioned in the superheater gas pass; a plurality of fluid heating tube banks including at least one reheater tube bank positioned in the reheater gas pass, said reheater tube bank being arranged upstream gas flowwise of the remaining fluid heating tube banks in said reheater gas pass; firing means associated with said furnace to produce heating gases for flow through the setting; a forced draft fan; an air inlet duct connected to the forced draft fan for delivering combustion air to said firing means; and tempering means for introducing a low temperature gaseous fluid through the second inlet of the convection gas pass, said tempering means including a tempering duct flow-connecting the air inlet duct to the second inlet of said convection gas pass.
 2. A ship propulsion system according to claim 1 wherein the tempering duct includes a damper for regulating the quantity of flue gas passing therethrough.
 3. A ship propulsion system according to claim 2 wherein the air inlet duct includes heat exchange means for heating the combustion air, the tempering duct being flow-connected to the air inlet duct downstream air flowwise of said heat exchange means.
 4. A ship propulsion system according to claim 2 wherein the air inlet duct includes heat exchange means for heating the combustion air, the tempering duct being flow-connected to the air inlet duct upstream air flowwise of said heat exchange means. 